A method according to the preamble of the base claim is known from the document U.S. Pat. No. 4,177,789 and from the corresponding foreign documents.
This document describes and shows a method for the production of very thin plates by the sawing of a block of marble, granite or similar stone material with a multi-blade frame. In this method, a block cut, as it were, "like a comb" is produced by means of a first multiple cut with a multi-blade frame and comprises a plurality of preliminary plates separated by fissures. A spacer material is then introduced into the fissures. A preferred spacer material in the known method is a setting fluid filler product, in particular a polyurethane foam. The fluid product is then left to set in the fissures, so as to form a solid spacer material.
After the spacer material has set, the known method proceeds to a second cutting by means of sawing with the same multi-blade frame. The second cutting takes place through the entire depth of the block along median planes of the preliminary plates, preferably so as to halve them in the sense of their thickness. During the second cutting, the spacer material which has set in the fissures prevents the preliminary plates from breaking.
Upon the completion of this operation, the known method produces a plurality of sandwiches formed by pairs of sheets, between which is a core of set resin and which are connected at one side by a part corresponding to the base of the block which was not cut during the first sawing.
In one case, these sandwiches are subjected to external finishing and then subjected to trimming operations to separate the final plates.
In certain circumstances, the same sandwiches could themselves constitute panels having two opposite, decorative outer faces. However, their structural strength is low due to the fact that the resin forming the core does not have good mechanical characteristics.
A first object of the invention is to provide a method which enables a sandwich of the type in question to be given mechanical strength such as to make it suitable for use as a structural panel with actual load-bearing characteristics.
This object is achieved by means of a method as defined in the characterising part of claim 1 and in the dependent claims 3 to 12.
By virtue of this concept, after the second cutting, a plurality of sandwiches are obtained directly from the block which are reinforced by a reinforcement constituted by the core and each of which, after surface finishing and any trimming of the edges, has two decorative faces and constitutes a panel which is both decorative and structural, that is, having mechanical strength, the latter characteristic being due to the reinforcement constituted by the core. Reinforced panels, for example, for the external cladding of buildings, can therefore be produced, the thickness and weight of which are much less than those of conventional cladding plates but which have much greater mechanical strength.
The resin used as the spacer material in the method known from the document U.S. Pat. No. 4,177,789 has binding properties with respect to the stone material, to ensure that the block becomes monolithic again in view of the second cutting. The two final plates of the sandwich are thus joined together by the spacer material. In order to obtain two separate, thin final sheets from the sandwich , their common part is removed by cutting and the central cutting of the resin core is then carried out. Finally, the remains of the resin of the core are removed from the corresponding faces of the final plates by a finishing operation.
Since these plates are very thin, perhaps only 5 mm thick, they are susceptible to breakage during the finishing and, moreover, if they are without reinforcement, they do not themselves have the necessary mechanical strength for certain applications. In one embodiment of the known method, respective reinforcing layers, which can also be heat-insulating or sound-absorbent, are applied to the outer faces of the sandwich to reinforce them. These layers may consist, for example, of one or more sheets of resin-impregnated glass fibres.
If the reinforcing properties are not required, the covering layers of the known method may be constituted by glass wool, expanded material, and the like.
The application of the covering layer to the faces of the individual sandwiches involves a certain expense which it would be desirable to reduce.
Another object of the invention is to produce panels constituted by a thin decorative plate which is reinforced so as to have good mechanical characteristics directly by a method similar to that of the document U.S. Pat. No. 4,177,789, but without the subsequent application of the reinforced covering layer.
According to the invention, this object is achieved by a method according to claim 2 and the subsequent claims.
This concept overcomes the prejudice whereby the central cutting of the preliminary plates could not be carried out safely, without breakage, in the absence of the intimate joining of the plates by means of a core of set material, such as a resin: in the document U.S. Pat. No. 4,177,789, an incoherent material, such as sand, was also proposed as the spacer material. Tests carried out with this incoherent material gave mediocre results, that is, an unacceptable percentage of breakages of the plates during the second cutting. This gave rise of the above prejudice.
Surprisingly, however, it has been found that when the fissures are filled at the same time with a reinforcing material and with a set filler product, particularly a resin which closes the structural gaps in the material, it is not in fact necessary for adjacent preliminary plates to be joined together intimately so that they do not shatter during the second cutting. On the basis of this fact, if a release layer or sheet is interposed in the filler material, composite plates or panels are obtained directly upon completion of the second cutting and after finishing, and are already provided with the reinforcement which, according to the known method, had to be applied by a separate operation. By virtue of the invention, this separate operation is eliminated with an obvious saving.
The preferred reinforcing materials will be specified in the course of the description with reference to the drawings. From the various possibilities, one which appears of great interest is that of the use of a sheet of glass or other transparent material as the reinforcing material. It is thus possible to produce plates like those described and illustrated in the document U.S. Pat. No. 4,640,850, but by a much more economical method than the one described in that document.